import { useCallback, useEffect, useRef } from "react";
import { useActiveAccountId } from "./activeAccount";

// Re-read per-account persisted state when this tab's active account becomes known (or changes). The
// provider tree above <App> mounts before the account is pinned, so its useState initializers seed from
// an unknown account (empty defaults); once <App> pins it, `rehydrate` runs to load the real stored
// value. Guarded so it never clobbers a value the user set in the brief pre-pin window: the returned
// `markDirty` is called by the owning setter, and a dirty state skips the re-hydrate.
//
// Keyed on the account id ONLY — the user's own writes go through setAccountRaw, which does not change
// the account id, so this effect can't loop on them.
//
// This is the localStorage-only counterpart of the `useEffect([me?.id])` server-prefs adopt pattern in
// FeedFiltersProvider / FeedViewProvider / PrefsProvider (and App's shell prefs): those re-load from the
// SERVER when the account query resolves; this re-loads from localStorage when the account is pinned.
// A provider needs one or the other — not both — to survive a fresh tab's first paint.
export function useAccountRehydrate(rehydrate: () => void): () => void {
  const accountId = useActiveAccountId();
  const dirty = useRef(false);
  const prev = useRef(accountId);
  // Latest closure in a ref so the effect depends on the account id alone (a fresh `rehydrate` each
  // render must not re-fire it), while still calling the current logic.
  const fn = useRef(rehydrate);
  fn.current = rehydrate;

  useEffect(() => {
    if (accountId === prev.current) return; // mount, and renders with no real transition
    prev.current = accountId;
    if (!dirty.current) fn.current();
    // Reset per account: `dirty` means "the user edited under THIS account". Today a real account
    // switch full-reloads (fresh instance), but clearing it here keeps the guard correct even if a
    // future switch stops reloading — the next account starts clean rather than inheriting dirtiness.
    dirty.current = false;
  }, [accountId]);

  return useCallback(() => {
    dirty.current = true;
  }, []);
}